I tried to open a PDF file today in XnView 1.98.2 never thinking that PDF would be a problem at this stage of the game. But, I got an error message "AFPL Ghostscript is not found on your system. please download it on http://www.ghostscript.com"

At ghostscript.com, I was/am totally confused about which version to use since there does not seem to be one called AFPL. The HELP wiki has no entries for AFPL or Ghostscript. So, here I am - reading a thread that started in 2004 and has a few recent entries.

I'm still confused - is GPL Ghostscript the one to use for the current version of XnView?
If so, then how do I decide on 32 bit vs 64 bit. My OS is Win 7 64 bit, but I seem to remember reading that XnView is a 32 bit application.

I suggest that the error message box be updated and an entry be added to the HELP Wiki (I'd do it if only I knew what to write)

While fiddling with other aspects of this topic, I also found the need to tick a box in Options...
Tools, Options, File List, on the "File List" tab (main part of the dialogue window has two tabs) in the column "Show as thumbnail" at intersection with row AI, PS, PDF... tick there. I did this and then they appeared.
I had previously been experimenting with GhostScript 32 bit and 64 bit so both are now in my system.